1. Field of Application
The present invention relates to an electronic control apparatus, such as a vehicle ECU (Electronic Control Unit), which incorporates a plurality of microcomputers, and in particular to an electronic control apparatus having a plurality of microcomputers and a microcomputer monitoring function.
2. Description of Prior Art
Types of vehicle ECU are known in the prior art which control an actuator of the vehicle engine, where the term actuator as used herein and in the appended claims signifies any device such as a throttle, fuel injection pump, etc., which affects the operation of the vehicle. The functions of such an ECU can include controlling the throttle position (i.e., degree of opening of the throttle valve) of the vehicle engine. In such an ECU, a microcomputer periodically calculates a target value of throttle position, based upon input parameters including the current accelerator position (i.e., degree of accelerator pedal actuation), and controls driving of a throttle motor for setting the actual throttle position in accordance with that target value. In that way, the throttle position can be controlled appropriately in accordance with the extent to which the accelerator is actuated by the driver of the vehicle.
It has also been proposed in the prior art to use an ECU having a main microcomputer which calculates values of throttle position as described above, and a auxiliary microcomputer which monitors the operation of the main microcomputer. In this case, the auxiliary microcomputer can monitor the main microcomputer to check that it is calculating appropriate values for the throttle position and is generating appropriate command values for operating the throttle motor, i.e., the auxiliary microcomputer checks that throttle control is being correctly applied.
The following methods could be utilized to perform such monitoring:
(1) Judging whether the actual throttle position that is established, based on calculated values of target throttle position, is within a predetermined range of normal values,
(2) Arranging that both the main microcomputer and the auxiliary microcomputer calculate each target throttle position, and judging whether both of these values coincide.
However in recent years, throttle control has become more complex, and it has become necessary to harmonize the throttle control function with other functions such as transmission control and traction control. In addition, the number of parameters used in performing a throttle control calculation have increased, and the calculation itself has become more complex. As a result, the contents of processing executed by the main microcomputer have become more complex. Hence, the monitoring function that is performed by the auxiliary microcomputer has become accordingly more complex. Thus the problem arises that, with prior art methods of monitoring, it is necessary to either decrease the accuracy of monitoring or to incur increased manufacturing costs for the monitoring equipment.
Specifically, if method (1) above is used for monitoring of throttle control, it becomes difficult to judge whether a change in the actual throttle position has resulted from an effect such as harmonization with some other type of control function, such as transmission control. Hence it becomes difficult to determine whether the actual throttle position is within a range of normal operation. Furthermore, if some factor other than the degree of accelerator actuation may affect the throttle position, it becomes necessary to extend the distance between the upper and lower limits of the range of degrees of throttle opening which corresponds to normal operation. Hence, the monitoring accuracy will be lowered.
On the other hand, if method (2) above is used for monitoring the throttle control, then the auxiliary microcomputer must have a similar level of processing performance to the main microcomputer, and all of the parameters which are required to calculate a throttle position must be supplied to the auxiliary microcomputer as well as to the main microcomputer, i.e., the auxiliary microcomputer must be capable of performing complex calculations. Hence the number of input ports required for the auxiliary microcomputer will be increased, and an increased level of processing functions and performance will be required for the auxiliary microcomputer. The cost of the auxiliary microcomputer will thereby be accordingly increased.
In addition, the software which is required for monitoring the main microcomputer will depend upon the type of vehicle control that is to be implemented. When there is a change in the vehicle control specifications, it is necessary to change the monitoring software accordingly. If method (2) above is utilized, this will result in increased development time being required for the monitoring software.